A method of this kind is known from U.S. Pat. No. 4,605,444. In this previously known method the mixture of casein and reagents is subjected to a chemical reaction and sterilization by the action of return elements during the build-up of pressure and temperature. Following the return elements there is also a conveying zone, at the end of which a further build-up of pressure occurs by virtue of an extrusion die. The basic product is extruded by this die.
A method is known from German published patent application No. 27 42 083, in which the product having a relatively low basic moisture content is processed, but a substance releasing inert gas is added by mixing to the mixture fed to the extruder, this gas being intended to have a protective gas effect on the product and to prevent thermal damage. In this previously known method no return elements are provided and an extrusion die is situated at the extruder outlet.
British patent specification No. 2,053,788 disclosed a mixing element which is arranged at the extruder end of a food extruder and which causes an interruption in the conveyed flow of material and is arranged ahead of the die on the discharge side.
In the known methods for the extrusion by boiling of caseinates extrusion takes place through nozzles bores, the lengths which are produced in this manner then being granulated. This calls for very high cutting speeds of over 4500 revolutions per minute. At the same time there is the risk of agglomerates forming in the protective hood during granulation at the discharge end.
Alternatively, extrusion can be effected through nozzle bores directly into a vacuum tunnel. The disadvantages of this method is that it is susceptible to trouble, e.g. during starting and cutting in the tunnel, and requires a relatively large amount of space.
Moreover, in the previously known method of water content of the product is, at 18 to 21%, relatively high so that it is difficult to achieve the desired ultimate consistency.